From the title I was expecting an usual pendulum experiment and no surprises, but I remembered a previous video about mixing hot and cold water, so I keep watching and got a surprise.
"Perhaps you should put a small part of http://www.youtube.com/watch?v=b7kRjHMzK5A&t=6m53s at the beginning of the video as a preview of the final result. "
Something like the movies that show a small part of an important scene at the beginning as a teaser.
It's difficult to try it at home because I have a 3yo that is too impatient. She would love something like this, but also cause a big mess that will be impossible to clean.